1. Field of the Invention
The present invention relates to a method and an apparatus for grinding a rotary body, and more particularly to such a method and apparatus which can be favorably employed for on-line grinding of a work roll in a rolling mill such as a hot rolling mill or the like.
2. Description of the Prior Art:
In the case where a web such as a steel plate or the like is subjected to hot rolling in a rolling line in which a large number of rolling mills are disposed in series, a work roll has a large tendency to wear compared to a backup roll. In particular, wear and surface roughening of a web-passage portion of the work roll coming into contact with a web are tremendous, and local wear of its portions corresponding to side edge portions of a web is remarkable. Hence, during rolling operation of webs, rolling was effected while regulating a sequence of widths of webs to be rolled such that rolling operations could be sequentially shifted from rolling of broad width webs to rolling of narrow width webs, the work roll was replaced periodically and after the worn work roll had been ground externally of the rolling mill, it was again assembled in the rolling mill to be used for further rolling operations.
However, in the above-mentioned process of carrying out the scheduled rolling in which a sequence of widths of webs is regulated so that rolling operations are effected sequentially from rolling of broad width webs to rolling of narrow width webs and the work roll is ground externally of a rolling line, a production efficiency is deteriorated due to constraints in the sequence of rolling operations moreover much labor is necessitated because the frequency of replacing the work roll is high. These deficiencies are a great cause of the lowering of an availability factor of an installation. Therefore, development of an on-line grinding method and an apparatus therefor in which grinding of a roll is carried out during the rolling operation while the roll remains assembled in a rolling mill, a period between roll replacements is prolonged, and rolling operations which are not retricted in their sequence by widths of webs, has been advanced.
Among the above-referred on-line grinding apparatuses in the prior art, apparatuses of the type shown in FIGS. 4(a), 4(b) and 10 to 12 are well known. More particularly, in the apparatus shown in FIG. 4(a), grinding is effected by pressing a rectangular-column-shaped block-like grindstone 1 against a work roll 2 that is being rotated. Also, in the apparatus shown in FIG. 4(b), grinding is effected by rotating a disc-shaped grindstone 3 by means of a motor not shown and pressing this rotating grindstone 3 against a circumferential surface of a work roll 2.
In the grinding apparatus employing the rectangular-column-shaped block-like grindstone 1 as illustrated in FIG. 4(a), while the structure is simple because there is no need to rotate the grindstone 1, there is a shortcoming in that since the grindstone 1 is not rotating, the grinding surface of the grindstone 1 is liable to be clogged by ground powder or to be baked, and moreover, since the grindstone 1 is rectangular-column-shaped, its corner portions are liable to be broken, hence its life is short and accidents are apt to be induced.
On the other hand, in the case of the grinding apparatus employing the disc-shaped grindstone 3 as illustrated in FIG. 4(b), while the life of the grindstone 3 is long and a grinding capability is excellent, since the grindstone 3 must be rotated, it is necessary to rotate a rotary shaft 4 of the grindstone 3 by means of a motor not shown. Accordingly, there is a shortcoming a that a large space along the longitudinal direction of the roll is necessitated, moreover in the case where a plurality of grindstones 3 are disposed, the distance between the adjacent grindstones 3 must be large, and it becomes impossible to grind the entire surface of the roll along its longitudinal direction.
In a grinding apparatus shown in FIG. 10, grinding is effected by pressing a rectangular-block-shaped grindstone 31 against a work roll 1' that is being rotated. In a grinding apparatus shown in FIG. 11, grinding is effected by positioning a grindstone shaft 5 of a disc-shaped grindstone 32 parallel to a work roll 1' and pressing the outer circumferential surface of the grindstone 32 against the work roll 1' that is being rotated, and in the illustrated example, a plurality of grindstones 32 are arrayed in the longitudinal direction of the work roll 1'. Furthermore, in a grinding apparatus shown in FIG. 12, grinding is effected by pressing an endless-belt-like grindstone 33 wound around a pair of rotating pulleys 4' against a work roll 1'.
In the case of the grinding apparatus employing the rectangular-block-shaped grindstone 31 as illustrated in FIG. 10, while the structure of the apparatus is simple because there is no need to rotate the grindstone 31, there is a shortcoming in that clogging of the grindstone 31 occurs frequently or the grindstone 31 is liable to be baked because the grindstone 31 is not rotating, and also that corner portions of the grindstone 31 are liable to be broken, resulting in a short life, because it is rectangular-block-shaped, and accidents are apt to be induced.
In the case of the grinding apparatus employing the disc-shaped grindstone as illustrated in FIG. 11, since the grindstone 32 is rotating, clogging would not occur, hence the life of the grindstone is long and a grinding capability is also excellent. However, in order to rotatably drive the grindstone 32 it is necessary to equip an electric motor not shown for driving the grindstone shaft 5, and therefore, there is a shortcoming in that a large space along the longitudinal direction of the work roll 1' is necessitated moreover in the case where a plurality of grindstones 32 are disposed, the distance between the adjacent grindstones must be kept large, and it would become impossible to grind the entire surface along the longitudinal direction of the work roll 1'.
Furthermore, in the case of the grinding apparatus employing the belt-like grindstone 33 as illustrated in FIG. 12, there is a shortcoming in that the grindstone is liable to wear and to be broken, and the apparatus is complex.